IGMP snooping proxying

As shown in Figure 13, to reduce the number of IGMP report and leave messages received by the upstream device, you can enable IGMP snooping proxying on the edge device. With IGMP snooping proxying enabled, the edge device acts as a host for the upstream IGMP snooping querier to send IGMP report and leave messages to Router A. The host IGMP report suppression mechanism on the edge device does not take effect. For more information about the IGMP report suppression mechanism, see "Configuring IGMP."

The IGMP snooping proxy device processes different IGMP messages as follows:

• General query.

  After receiving an IGMP general query, the device forwards the query to all ports in the VLAN except the receiving port. The device also generates an IGMP report based on the local membership information and sends the report to all router ports.

• Group-specific query or group-and-source-specific query.

  After receiving an IGMP group-specific query or group-and-source-specific query, the device forwards the query to all ports in the VLAN except the receiving port. If the forwarding entry has a member port, the device sends a report to all router ports in the VLAN.

• Report.

  After receiving an IGMP report from a host, the device looks up the forwarding table for a matching entry as follows:

  • If a match is found and the matching forwarding entry contains the receiving port, the device resets the aging timer for the port.

  • If a match is found but the matching forwarding entry does not contain the receiving port, the device adds the receiving port to the outgoing interface list. It also marks the receiving port as a dynamic member port and starts an aging timer for the port.

  • If no match is found, the device creates a forwarding entry with the receiving port as an outgoing interface. It also marks the receiving port as a dynamic member port and starts an aging timer for the port. Then it sends the report to all router ports.

• Leave message.

  After receiving the IGMP leave message on a port, the device sends an IGMP group-specific query through the receiving port. The device sends the IGMP leave message to all router ports only when the last member port is removed from the forwarding entry.